1) 2 months should be good, 1oz wont get overly oaky to have to fret tasting it that often
2) i wouldnt. if you want it sour, i'd add some dregs to it and wait another 6-12 months. is the sweetness just from the raspberry or the beer itself?
btw, 644 is brux trois, very different than brett brux. in any case it wouldnt be sour just from using brett.
also was this a 644 primary or secondary? if primary, this was finished months ago